As exemplified by the terrorist attacks in the United States on Sep. 11, 2001, the increasingly frequent acts of terror internationally dictate the importance of risk management for freight containers that are transported by aircraft, ships, freight trains and trucks. The possibility exists that a terrorist could secrete a nuclear weapon, explosives, poison gas, a biological weapon, or a radioactive substance into a freight container and send it anywhere. Freight containers are used to ship a wide variety of products and raw materials. It has been estimated that 18 million containers arrive in the United States annually. Currently, only about 2% of those are inspected. There are cases in which X-rays can be used from the outside of the container and the resulting image can be analyzed to identify dangerous items that have been secreted therein. In addition, radiation detectors and odor sensors can also be used to identify some dangerous articles. However, considering the diversity of possible threats and the number of ways that dangerous articles can be packaged to appear innocuous, it must be concluded that detection of dangerous articles is not possible in most cases. It must further be considered that dangerous articles are not always secreted into containers after they are closed, these articles could be placed into the container in the first place, or containers can be swapped out for others. Theft of cargo from containers has long been a problem, but there exists a clear risk that such theft rings can work in league with terrorists to secrete dangerous articles into the containers even as they steal cargo from them. Since it is not easy to use sensors to check cargo for danger, there are movements afoot to check the reliability of the shippers to evaluate the risk of the cargo they load. However, an empty container, which has no shipper, cannot be evaluated based on the reliability of a shipper. Since the demand for container transportation of cargo is not stable, varying by geographical area and the season of the year, there are many cases when empty containers must be transported among many countries by air, ship, rail and truck. This transportation of empty containers brings no profit to freight shippers, and accordingly, there is a strong tendency to avoid the cost of security measures when shipping empty containers. Thus, there is a high possibility that an empty container could be used as a terrorist tool. It follows that the surveillance and reporting of any unauthorized opening of an empty container's doors or walls is a very important anti-terrorism measure. To wit, as anti-terrorism measures, it is necessary to (1) monitor and report any unauthorized access to the inside of a container be it loaded with cargo or empty, and (2) to detect and report any swapping of containers.